This invention relates generally to wireless communication systems, and more particularly, to communicating location information with wireless communication systems, especially using a public safety band for transmissions.
Public safety communications are provided over specified communication frequencies. Public safety transmissions may be provided using, for example, a land mobile radio (LMR), which may be used to transmit public safety communications between different mobile units, for example, different LMRs. Land mobile radio band communication including public safety radio communication (e.g., police, fire department, etc.) is generally available within the VHF, UHF, 700 MHz and 800 MHz frequency bands. Part of each of these frequency bands is allocated by the Federal Communications Commission (FCC) for public safety communication services and is also referred to as Public Safety Frequency Bands. These public safety communications also may be provided using private land mobile radio services (PLMRS).
The radios communicating the public safety transmission may use different communication protocols or standards when transmitting. For example, an LMR standard such as Project 25 or Terrestrial Trunked Radio (TETRA) communication standard may be used to communicate public safety transmissions. These radios also may have the capability to communicate other information. For example, these radios may be equipped or have the option to add on a Global Positioning System (GPS) receiver or module. The GPS enabled radio is then able to transmit position information regarding the location of the radio and provides a tracking feature. However, adding a tracking system (with a GPS unit) often requires expansion of the communication system to handle the increased data from the GPS transmissions. Thus, added controls are needed to balance the radio network loading while trying to accurately track the radios. In some circumstances, for example, where a large number of radios are in the same geographic area and communicating using the same communication site, the voice data communication in addition to the location information transmission can overload the system and cause communications to fail.
Known systems attempt to balance the transmission of voice and data, including position updates, by transmitting position updates (e.g., a short position message) at a slow rate. For example, position updates are communicated every fifteen minutes or every thirty minutes and then may be displayed at a dispatch center. However, this information provides coarse location information that may be inaccurate depending on the movement of the radio. For example, if a high speed chase is in progress, location information communicated even at one minute intervals can be inaccurate.
Thus, these known radios and systems that provide communication and location information often require additional controls for managing the location information data transmissions. These added controls add cost and complexity to the system. Additionally, the location information is often coarse and may even be inaccurate as a result of the time between location transmissions.